1. Field of the Invention
This invention relates generally to heat exchangers, and more particularly to an arcuate heat exchanger which engages the exterior of fluid pump motors and utilizes the heat produced by the motor to heat fluid circulated through the heat exchanger.
2. Brief Description of the Prior Art
Most spas, hot tubs, and therapy tubs which utilizes jet nozzles to circulate water to the tub have a circulating system utilizing a motor with a centrifugal pump which takes a suction from the bottom of the tub and delivers the water through an electrical heat exchanger, or heater, to the discharge nozzles in the tub. The electrical heaters have heating elements which wear out and have electrical wires which may become grounded. The heater is controlled by a thermostat which regulates the tub water temperature. The Consumer Products Safety Commission states that the maximum temperature for a hot tub should not exceed 104.degree. F.
The commonly used thermostat is only accurate to within 3.degree. F. A person in the tub will usually experience an uncomfortable cooling effect as the water reaches the lower limit (less than about 100.degree. F.) to activate the heater, and then an uncomfortable rise in the water temperature as the heated water is discharged through the nozzles. Thus, the occupant is subjected to an endless cycle of cooling and heating as the heater cycles on and off. The constant cycling of the heater consumes significant energy and is expensive to operate.
The electric motor which powers the pump circulating the water produces heat during its operation which is roughly proportional to its horsepower rating. Typically, the coil of the motor will reach a temperature of about 196.degree. F. and the motor housing or casing will reach a temperature of about 155.degree. F. However, this energy is dissipated into the atmosphere by the motor casing and is wasted.
The present invention provides a means of recovering the wasted heat energy of the motor and utilizes it to heat the water being pumped and circulated to the tub. Thus, eliminates the need for an electric heater which results in conservation of energy, reduction in the cost of operation of the heated tub, and maintains the tub water at a substantially constant and comfortable temperature.
The pumps used in water circulation systems in the pool and spa industry are required to be of the "100% drain" type. In other words, the system including the pump must completely drain all water out of the system to prevent growth of bacteria. The high pressure side of the pump is referred to as the discharge end and the low pressure side is referred to as the intake, or suction end of the pump. The standard combination pump/motor has the high pressure (discharge) connection above the mid-point (usually at the top) and above the low pressure (intake) pump connection.
The present invention utilizes the suction end of the pump to completely drain the water from the heat exchanger, thus the heat exchanger in accordance with the present invention and meets the "100% drain" requirements of industry regulations.
There are several patents which disclose various heat exchange apparatus for motors, most of which are directed toward devices which merely cool an electric motor.
White, U.S. Pat. No. 3,127,530 discloses a cooling apparatus for motor driven pumps wherein the motor is of the type having a cooling fluid internally circulated within the rotor chamber of the motor. A sheet metal casing is installed around the motor housing and cooling fluid is pumped through the casing to cool the motor. Alternatively, if additional cooling is required, a length of tubing bent in a serpentine coil with fittings at each end is placed between the motor housing and the sheet metal casing and the hot fluid from the internal cooling circuit of the motor is recirculated through the coiled tubing and exposed to the cooling fluid in the casing and back to the rotor chamber.
Onsrud, U.S. Pat. No. 2,862,120 discloses a fluid cooled electric motor housing. The housing or casing of the motor is a pair of concentric annular steel shells supported in spaced relation by a plurality of longitudinal, circumferentially spaced baffle ribs welded therebetween.
Bone, U.S. Pat. No. 4,516,044 discloses a motor cooling apparatus comprising a single piece or two-piece metal housing having a cylindrical cavity which surrounds the exterior of the motor. The side wall of the cylindrical cavity is provided with a series of pairs of parallel circumferentially incomplete grooves joined together at one end and enclosed by the exterior of the motor casing to form a water channel for cooling the motor.
Vandenbossche, U.S. Pat. No. 4,213,498 discloses a plastic heat exchanger which can be tightly faced on a cylindrical member to control the temperature of the member which comprises two plastic sheets separated by a plurality of parallel ribs fused thereto to form a plurality of channels, rectangular in cross section, and a pair of cylindrical channels connected at each end of the channels normal to the axis of the channels. The outer plastic sheet is provided with a layer of insulating foam.
Williams, U.S. Pat. No. 4,854,373, discloses a crescent shaped heat exchanger made of welded sheet metal plates conforming to the shape of the motor. The longitudinal (bottom) edges of the heat exchanger are inclined in opposite directions relative to a horizontal plane passing through the longitudinal axis. In other words, one side slopes downwardly from front to back and the other side slopes downwardly from back to front. The lower end of each longitudinal end plate has a port so that water will drain toward both ports and water can be introduced through one port and discharged through the other. Since one pair of diagonally opposed corners of the heat exchanger are lower than the other diagonally opposed corners, the arc subtended by the inner curved plate is slightly greater than 180.degree. when viewed transversely. This configuration is suggested to allow the device to snap fit onto the upper surface of the motor. However, the welded sheet metal construction would make this extremely difficult or impossible.
Because the Williams heat exchanger subtends slightly more than 180.degree. past the mid-point of the pump motor, and both the intake and discharge ports are at the lowest point, one side of the Williams device would not drain when connected to pumps in accordance with the industry standard, since the standard motor driven pump has the high pressure (discharge) connection above the mid-point of the motor (usually at the top) and above the low pressure (intake) pump connection to meet the 100% drain requirement. Williams requires drilling and tapping the pump to make connections to the intake and discharge ports of the jacket, rather than being able to use the existing pump ports.
The present invention is distinguished over the prior art in general, and these patents in particular by a heat exchanger for use in combination with motor driven fluid pumps of the type having a motor with an outwardly curved upper surface. The heat exchanger has an arcuate heat exchange jacket formed of an inner wall, an outer wall, and a spacer frame sealed therebetween which has an open center section defining a hollow enclosed cavity. The jacket is configured to engage the exterior surface of the pump motor for maintaining heat exchange contact between the pump motor and the cavity. The jacket has a fluid inlet and one or more outlets. A venturi cross having a pair of tubular extensions may be connected to the intake port of the pump with one extension connected to the jacket inlet and the other extension to the jacket outlet to subject the jacket to negative pressure created by the venturi cross to draw a portion of the fluid through the jacket cavity and recirculate it through the pump. Alternatively, a cross having a pair of tubular extensions may be connected to the intake port of the pump and both extensions connected to a pair of jacket outlets in combination with a supply tee connected to the high pressure discharge conduit and to the jacket inlet to subject the jacket to the pressure differential between the pump intake port and the pump discharge port to pass a portion of the pressurized fluid through the jacket cavity and recirculate it through the pump. The supply tee may contain a thermostat to open and close fluid flow through the jacket.